In the production of methacrylic acid by gas phase oxidation of methacrolein in the presence of a catalyst, the catalyst is generally a heteropoly acid catalyst.
U.S. Pat. No. 4,301,031 (registered on Nov. 17, 1981) describes that the catalyst produced from heteropoly acid slurry having the composition of Mo12P0.1-3M0.1-3Cu0.1-2V0.1-2X0.01-2YaOb (Wherein, M is K, Rb or Cs; X is Ba, La, Ga, Al, Ag, Cd, Ti, Tl, Hg, Pb or Zn; Y is Fe, Co, Ni, Sr, Mn, In, Ta, Ge, S or Be) by the processes of drying the slurry without using nitric acid, molding and firing is effective in oxidation of methacrolein.
U.S. Pat. No. 6,458,740B2 (registered on Oct. 1, 2002) describes a method of preparing a catalyst which comprises the steps of mixing ammonium paramolybdate and ammonium methavanadate with pyridine and 85% phosphoric acid; adding nitric acid, cesium nitrate and copper nitrate to the above mixture, followed by coprecipitation; heating and drying the mixture to give a catalyst.
U.S. Pat. No. 4,621,155 (registered on Nov. 4, 1986) describes that a catalyst prepared by using a material containing nitrogen such as pyridine, piperidine or piperazine has excellent plasticity and physical strength and reproducibility in catalyst production. But, to produce such a catalyst, pre-firing in the presence of nitrogen is necessary before air firing, in order to prevent structural disassembly by rapid heating during air firing, resulting in inefficiency.
Japanese Patent No. 3772389 (published on Nov. 25, 1997) describes a method of preparing a heteropoly acid catalyst from heteropoly acid produced from molybdenium oxide, vanadium oxide and phosphoric acid by the processes of mixing with ammonia water and zinc oxide, drying and firing thereof.
However, the catalysts prepared by the above methods have a problem of low conversion rate and low selectivity during gas phase oxidation of methacrolein, which needs to be improved.